The main objectives of this research are to study the effects of various factors such as physiological (age, sex, nutrition, hormones), genetic (species, strain) and environmental (insecticides, carcinogenic polycyclic hydrocarbons) on the enzymes metabolizing xenobiotics in various tissues, especially intestine. The current projects under study concern (1) hormonal regulation of xenobiotic-metabolizing enzymes in various species and strains of laboratory animals, (2) study of xenobiotic-metabolizing enzyme systems in rabbit small intestine and the comparison with similar systems in liver-effect of environmental pollutants on those systems, and (3) genetic regulation of induction of xenobiotic-metabolizing enzymes in various strains of mice.